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Capacity Design of Foundation Beams to EC8

Capacity Design of Foundation Beams to EC8

Capacity Design of Foundation Beams to EC8

(OP)
Hello fellow engineers,

I need help on how to proceed with the design of RC foundation beams of a two storey RC frame house.
I have designed the beams and columns in capacity design and now i need to capacity design the foundations.
The foundations are comprised of a monolithic foundation slab(raft) with foundation beams interconnecting the columns. see pictures below


Ok, lets start with the question

1. I have already capacity designed the superstructure using the action effects derived from the linear analysis using the deign response spectrum to represent the seismic action.
Shall I use the same analysis results and continue with the capacity design of the foundation beams or do i need to run a second analysis with a decreased behaviour factor?
(keep in mind that i want to use capacity design)











The way i want to proceed is to initially design the foundation beams on their own neglecting the contribution of the foundation slab.
I will take that into consideration once the beams are designed on their own



RE: Capacity Design of Foundation Beams to EC8

(OP)
I finally managed to get my head around one of the texts, this is what i found.

Capacity Design of Foundation Beams and Soil to EC8

Design Approach 1 (DA1):

1. Reduce the behaviour factor q used in the capacity design of the superstructure by 40%.
2. Run the analysis using the reduced behaviour factor qrd.
3. Design the soil and foundation beams in accordance with the new magnified action effects.
4. Foundation beams don't need to be detailed for ductility or capacity designed for shear.
5. Detail them according to EC2.

Design Approach 2 (DA2):

a) Design of foundation Beams

1. No modification is applied to the behaviour factor q used in the capacity design of the superstructure.
2. Run the analysis using the same unmagnified behaviour factor q.
3. Dimension and detail foundation beams using capacity design rules for beams of the same ductility class.

b) Design of soil

1. Reduce the behaviour factor q used in the capacity design of the superstructure by 40%.
2. Run the analysis using the reduced behaviour factor qrd.
3. Design the soil in accordance with the new action effects.

RE: Capacity Design of Foundation Beams to EC8

(OP)
Anyone have something to add to my findings, i am really interested to see what you guys think.
or maybe you could comment on the procedure you follow so that we may compare.

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